1. 在VB中，将一个二进制数转化成十六进制的自定义函数代码如下，请在程序划线处填入合适的代码。

Function btoh(s As String)As String

Dim i As Integer, s1 As String, t As Integer

Dim str As String, j As Integer

str="0123456789ABCDEF"

i= Len(s)

Do While i >=1

If    ①     Then

s1= Mid(s, i－3, 4)

Else

s1 = Mid(s; 1, i)

End If

t=0

For j =1 To Len(s1)

t=    ②  

Next j

btoh = Mid(str, t + 1, 1)+btoh

i=i－4

Loop

End Function

① ②